656
October 2017
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
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Publisher ASPRS
Editor-In-Chief Alper Yilmaz
Technical Editor Michael S. Renslow
Assistant Editor Jie Shan
Assistant Director — Publications Rae Kelley
Electronic Publications Manager/Graphic Artist Matthew Austin
Photogrammetric Engineering & Remote Sensing
is the official journal of the
American Society for Photogrammetry and Remote Sensing. It is devoted to the
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Information Systems, Photogrammetric Applications, Lidar, Primary Data
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When a massive iceberg first broke away
from Antarctica’s Larsen C ice shelf some-
time between July 10-12, 2017, scientists
knew it would eventually start breaking
apart. That’s the normal life cycle of a
drifting iceberg, which is at the mercy of
the ocean’s battering currents, tides, and
winds. Already those forces have turned
A-68 into two named bergs, A-68A and
A-68B, as well as a handful of pieces too
small to be named by the U.S. National Ice
Center.
In the two weeks following the initial
break, satellite imagery has documented
the iceberg’s motion. The southern end ap-
pears to have slammed into a mix of float-
ing ice above Gipps Ice Rise—the bump of snow- and ice-covered bedrock visible in
the lower right of the image. Then the berg rebounded and its northern end swung
back toward the just opened rift. The resulting impact caused both the berg’s north
end and the ice shelf to fracture.
“The back-and-forth movement of A-68 looks akin to maneuvering a parallel-parked
car out of a tight parking space—like an Austin Powers three-point turn,” said Chris-
topher Shuman, a cryospheric scientist at NASA’s Goddard Space Flight Center and
the University of Maryland, Baltimore County.
The fractured berg and shelf are visible in this image, acquired on July 21, 2017, by
the Thermal Infrared Sensor (TIRS) on the Landsat 8 satellite. The false-color view
shows the relative warmth or coolness across the region. White indicates where
the ice or water surface is warmest, most notably in the widening strip of mélange
between the main iceberg and the remaining ice shelf. Dark grays and blacks are
the coldest areas of ice.
So far, the calving and fracturing has taken place under the dark cover of polar night
during Antarctica’s austral winter. That makes thermal imagery from satellites a
critical tool for “seeing” the action. Adrian Luckman of the UK-based Project MI-
DAS first saw the berg break away in thermal data from the Moderate Resolution
Imaging Spectroradiometer (MODIS), before Sentinel radar data became available
later on July 12.
The thermal view above shows a remarkable amount of detail. The bright signature
of relatively warm ocean water appears around A-68B, which broke off sometime
between late July 13 and early July 14. More subtle fractures north of A-68B are
visible on the shelf; these pieces will eventually break free and move out to sea with
the rest of the ice.
All of the ice pieces large and small are subject to the water currents of the Weddell
Gyre and the strong weather systems that can whip up blinding snow and blanket
the region in clouds for many days at a time. This same ocean circulation that will
eventually move the bergs northward toward South Georgia Island.
NASA Earth Observatory images by Jesse Allen, using Landsat data from the U.S.
Geological Survey. Story by Kathryn Hansen.
This image record originally appeared on the Earth Observatory.
To see the full image, visit,
